Caveat: This is a bit nit-picky, but important nonetheless.
I've had a few people ask me how to listen to my podcasts in iTunes - when subscribed, they get the latest one, but they can't see how to get any more.
Here's the problem: iTunes on Windows looks like a Mac application, and some of the standard Mac widgets aren't recognized by Windows users.
Once you've subscribed to a podcast, you can go to the podcasts section in iTunes and see the ones that you've subscribed to. The problem is that, for a Windows user, it's not obvious that you have to click the grey triangle to expand it, or that it's expandable at all.
Discoverability and following standard concepts for the platform are features of good UI design. Windows users are used to seeing the plus and minus symbols for expandable lists, not triangle thingies that have no obvious meaning.